Electrophotographic method for producing an image on dielectric film using ion generation

ABSTRACT

An electrophotographic method, in which a dielectric film is contacted with a surface of a charged and exposed electrophotographic layer and said film is acted on by positive and negative ions of the same concentration from a source of ions, which settle on the film and produce a latent image thereon. Then the electrophotographic layer is illuminated by an actinic light source to preserve the latent image on the film and the film is separated from the electrophotographic layer while being illuminated or after that. Thereafter the latent image obtained on the film is developed and fixed.

TECHNICAL FIELD

The present invention relates to the field of producing of visibleimages by means of an electrophotographic method using electrostaticcharged images. More particularly, the invention relates to methods ofobtaining a picture on a dielectric film.

BACKGROUND OF THE INVENTION

The known electrophotographic methods for obtaining a picture on filmsare based on transfer of a latent image from a charged and exposedselenium layer onto a dielectric film by producing a gas discharge inthe air gap between the selenium layer and the dielectric film (U.S.Pat. No. 2,937,943, published on May 24, 1960).

This method has insufficient resolution. The picture thus obtained isblurred due to scattering of ions in the gas-discharge gap.

Furthermore, when developing the wide fields on the transferred latentimage a marginal effect is observed, as well as on the exposed seleniumlayer. The value of the charge of the transferred image is different forthe image elements of different width. Therefore, during the developmentthe optical density of the image elements is different.

Known in the art is a charge-free method for obtaining an image on adielectric film, in which the dielectric film is brought in contact withsurface of a charged and exposed electrophotographic layer, then thefield of the latent image is developed and fixed (cf. R. Shaffert"Electrophotography", "Mir" publishers, Moscow, 1968, p.p. 323-333).

In this discharge-free method the image is sharper than in theabove-mentioned method, however, it is still inadequate for practicalpurposes. This is associated with a decrease in the gradient of thefield intensity at the boundaries of the fine lines on the film surfaceto the refraction of the field line in the film.

Like in the methods based on a gas discharge, the discharge-free methoddoes not suitable for producing an image with wide fields without fringeeffect. Furthermore, the optical density of the image elements ofdifferent width is also not constant.

All this hinders utilization of the images obtained for making copies onthe light-sensitive layer of an offset plate. Furthermore, the abovedescribed method does not allow one to obtain several images using aonce-exposed electrophotographic layer.

DISCLOSURE OF THE INVENTION

The main object of the invention is to develop an electrophotographicmethod for producing an image on a dielectric film, in which productionof a latent image on the film, which is a bipolar system of chargeslocated in the same plane, would make it possible to improve thesharpness of the edge of the fine lines of the image and to eliminatethe fringe effect.

This object is attained by providing an electrophotographic method forproducing an image on a dielectric film, in which the dielectric film iscontacted with the surface of a charged and exposed electrophotographiclayer, the image produced on the film being developed and fixed;according to the invention, after the dielectric film has been broughtin contact with the electrophotographic layer, the dielectric film isacted on by positive and negative ions of the same concentration from anion source; the ions settle on the film and produce a latent imagethereon; prior to developing this image the electrophotographic layer isilluminated by an actinic light source.

During and after the illumination of the electrophotographic layer bythe actinic light source, it is expedient to separate the dielectricfilm from the electrophotographic layer for eliminating the fringeeffect during subsequent development of the once reproduced latentimage.

The object of the invention is also attained due to the fact that in theelectrophotographic method for producing an image on a dielectric film,in which the dielectric film is contacted with the surface of a chargedand exposed electrophotographic layer; the latent image is developed andfixed; according to the invention, after the dielectric film has beenbrought in contact with the electrophotographic layer, the dielectricfilm is acted on by positive and negative ions of the same concentrationfrom a source of ions, which settle on the film and produce a latentimage thereon; after that the dielectric film is separated from theelectrophotographic layer illuminated by a non-actinic light source toeliminate the fringe effect during the subsequent development of themultiple-reproduced latent image.

The charge of the latent image on the dielectric film is preferablyincreased by raising the potential of the charge of theelectrophotographic layer, in which case the dielectric film isseparated from the electrophotographic layer in an electrically inertmedium preventing a discharge between this film and theelectrophotographic layer.

It is expedient to use the chlorine derivatives or fluochloroderivativesof hydrocarbons of the aliphatic group as an electrically inert medium.

The electrophotographic method of producing an image on a dielectricfilm makes it possible to improve the quality of the image, i.e. toincrease the sharpness of the edges and the resolution when developingthe latent electrophotographic image on dielectric films of up to 100 μmthick. The method makes it possible to completely eliminate the fringeeffect when reproducing images containing continuous sections of anysize and to obtain a few images on the films after reproducing theoriginal only once.

Furthermore, the method increases the optical density and contrast ofthe image on diapositives while providing uniform reproduction ofcontinuous fields.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 shows a selenium layer on a metal substrate carrying a positivelycharged latent electrostatic image;

FIG. 2 is the same as in FIG. 1 with a dielectric film on a seleniumlayer;

FIG. 3 is the same as in FIG. 2, with a source of ions settling on thedielectric film in accordance with the operation of compensation of thefield of charges of the latent image on the selenium layer, according tothe invention;

FIG. 4 shows a dielectric film with ions settled thereon, said filmbeing located on a selenium layer illuminated by an actinic light sourcein accordance with the operation of destruction of the latent image onthe selenium layer, according to the invention;

FIG. 5 shows a dielectric film located on the selenium layer afterdestroying the latent image on this layer, according to the invention;

FIG. 6 is the same as in FIG. 5, with a layer of a developingcomposition on the dielectric film, according to the invention;

FIG. 7 shows a dielectric film with a developed image located on theselenium layer and a device for fixing the image, according to theinvention;

FIG. 8 shows a film with an image obtained, according to the invention;

FIG. 9 shows a dielectric film with ions settled thereon, said filmbeing separated from the selenium layer when illuminated by anon-actinic light source in accordance with the operation of separation,according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The electrophotographic method for producing an image on a dielectricfilm is effected as follows.

A dielectric film 3 (FIG. 2) is applied on a charged and exposedelectrophotographic layer, in this embodiment--a selenium layer 1(FIG. 1) applied on a metallic substrate 2. The dielectric film isapplied on the selenium layer in a vacuum chamber and is brought incontact with the entire surface of this selenium layer 1. After that,the dielectric film 3 is acted on by positive and negative ions of thesame concentration from an ion source 4 (FIG. 3), which is located abovethe film 3. Used as a source 4 are well known static eliminators of theradioisotope type or neutralizers with a corona or slide discharge. Inthe latter case the identical concentration of ions of differentpolarity in the space between the film 3 and the outlet of the source 4is provided by properly selecting the supply current.

When the film 3 is acted on by ions of different polarity, these ionssettle on the film 3 and the portions of the film 3 located, forexample, above the positively charged latent image on the selenium layer1 acquire a negative charge, while the portions located above the blankelements of the latent image acquire a positive charge. In other words,the action of the ions of different polarity results in completeneutralization of the field of the latent image above the film 3 and inproduction of a latent image on the film 3 itself.

After the film 3 has been acted on by the flow of ions, the ion source 4is removed. In order to obtain an electrical field of charges on thelatent image above the film 3, the selenium layer 1 is illuminated by anactinic light source 5 (FIG. 4), e.g. by an ordinary incandescent lampor by a fluorescent lamp. In so doing, the latent image on the seleniumlayer 1 (FIG. 5) is destroyed while on the film 3 the image on the film3 remains intact.

After illuminating the latent image on the selenium layer 1, theobtained latent image on the dielectric film 3 is developed. For thispurpose, a developer 6 (FIG. 6) is applied onto the surface of the film3. In the proposed method any known developer can be used, i.e. liquid,dry or aerosol. Liquid developers are preferable, since they provide animage of higher quality than all other compositions.

After removing the residues of the developer 6 from the surface of thefilm 3, the developed image is fixed depending on the type of thedeveloper 6 through a device 7 (FIG. 7) for fixing the image. After thefixing the film 3 (FIG. 8) is a finished diapositive.

The latent image produced on the film is featured by high gradient ofintensities in the boundary regions of the charges and this makes itpossible to improve edge contrast and, therefore, the resolution of themethod in general. Furthermore, the presence of charges of a latentimage on the film makes it possible to remove the film from the seleniumlayer after the process of development without waiting until the imageis fixed. This allows one, for example, to conduct thermal fixing ofpowdery imagess without contacting the film to the layer.

When the proposed method is used for obtaining images having widecontinuous fields, the dielectric film 3 is removed from the seleniumlayer 1 (FIG. 9) during or after the illumination of the selenium layer1 by an active light source 5 (FIG. 4). Then a suitable developer isapplied onto the surface of the film 3 and the latent image is developedand fixed. These operations are effected as described above.

The separation of the film results in an increase in the potential ofthe latent image charge. Furthermore, the field intensity above themiddle and edges of a continuous field becomes the same. This allows oneto reproduce continuous fields with uniform density after thedevelopment.

Thus, the separation of the film during the illumination of the seleniumlayer makes it possible to obtain a once reproduce latent image withouta fringe effect.

In order to eliminate the fringe effect when reproducing the imagecontaining continuous fields of any size and to obtain a few images onthe films after one reproduction of the original, the film 3 (FIG. 4) isacted on by bipolar ions thus completely compensating the field of thelatent image and by subsequently separating the film 3 (FIG. 9) with thelatent image from the selenium layer 1 using a non-actinic light source8. When the film 3 is separated from the layer 1, the field intensityabove the medium portion and edges of the continuous section increasesand becomes constant. This makes it possible the following developmentto reproduce continuous fields with uniform density regardless of theirsize. Since the film 3 is separated while being illuminated by anon-actinic light source, the latent image on the selenium layer 1remains intact. This allows one to repeate the above described operationof obtaining an image until the potential of the selenium layer dropsbelow permissible level due to dark discharge.

In order to increase the optical density and contrast of the image ondiapositives with uniform reproduction of continuous fields, the chargeof the latent image on the film 3 (FIG. 9) is intensified by increasingthe charge potential of the charge of the selenium layer 1. In thiscase, like in the case of producing a once-reproduced latent image andin the case of producing a multiple-reproduced latent image, theseparation of the film 3 is effected in an electrically inert mediumpreventing origination of discharges between the film 3 and the seleniumlayer 1. The chloride derivatives of hydrocarbons of the aliphaticseries or fluorochlorine derivatives of hydrocarbons of the same seriesare used as an electrically inert medium.

Separation to the film in an inert medium makes it possible to increasethe potential of the selenium layer to 1000 V and to increase theoptical density D of the lines of the dispositive to 3.5 with a contrastcoefficient γ of up to 15.

For better understanding of the electrophotographic method for producingan image on a dielectric film specific embodiments of the invention aregiven hereinbelow by way of example.

EXAMPLE 1

A lined original--a positive with optical density of the image of 1.45and that of the background of 0.2--is reproduced in a copying apparatus.A selenium plate with a layer 50 microns thick is charged with apositive charge in the processor of the apparatus to a potential of 600V and then is exposed during 35 seconds with an aperture of 1:22. Theexposed plate is transferred into a room with non-actinic lighting andplaced into a vacuum chamber, where a sheet of triacetate film 25microns this is laid into the selenium layer. After a complete contactof the film with the entire surface of the selenium layer has beenachieved, a radioisotope static eliminator is placed above the seleniumlayer at a distance of 30 mm and kept therein during 5 to 10 seconds.After that the selenium layer is subjected to general illuminationduring 2 seconds by a 75-W incandescent lamp, which is located at adistance of 1 m from the selenium layer.

The image is developed by means of a dry electrophotographic developerusing a magnetic brush. The film with a developed positive image is thenremoved from the selenium layer and the powder is thermally fixed byholding it in a thermostate. The blurriness of the obtained image iswithin 5-10 μm, while that of the image obtained by the known method itis equal to 50-75 μm.

EXAMPLE 2

The lined original is reproduced as described in Example 1 but thedevelopment is effected by means of a liquid electrophotographicdeveloper for negatively charged images. The developer is fed into thespace between the external surface of the film and a flat metalelectrode located at a distance of 1 mm from the film. After thedevelopment the image is dried by an air stream. The blurriness of theobtained image is practically absent. The blurriness of the imageobtained by the known method is 40 μm.

EXAMPLE 3

A diapositive image is produced from a negative original. The image isproduced on a film by projecting the negative picture on a 50-μm layerby means of an enlarger. The selenium layer is charged with positivecharges from a corona-arc discharger to a potential of 600 V. Theexposure is made during 3 seconds with an aperture of 1:16 and anincandescent lamp 100 W. Then all subsequent operations are conducted,similar to those described in Examples 1 and 2, then the latent image isdeveloped by a liquid developer for positively charged images. As aresult, a diapositive is produced which practically has no blurriness.

Compared to the known methods, the use of the proposedelectrophotographic method for producing an image described in Examples1 to 3 provides much higher sharpness of the image, which is especiallyimportant in printing-plate processes of polygraphic industry; highreproducibility of the obtained results under any climatic conditions;high economy of the process due to an increase in the working capacityof the selenium layers.

EXAMPLE 4

A lined positive original having optical density of the image of 1.45and that of the background of 0.15 is reproduced by means of aprojector. The selenium layer 50 μm thick is charged positively to apotential of 100 V and then exposed during 60 seconds with an apertureof 1:22. The exposed plate is placed into a room with non-actinic light,where the selenium layer of the plate in a vacuum frame is covered by asheet of triacetate film 25 μm thick. After the complete contact of thefilm with the entire surface of the selenium layer has been achieved, aradioisotope static eliminator is placed above the selenium layer at adistance of 30 mm for a period of 5-10 seconds, the body of the staticeliminator being connected to the substrate of the selenium layer. Thenthe selenium layer is exposed to the light of an incandescent lamp100-75 W during 1 to 2 sec. The distance between the lamp and seleniumlayer is equal to 1 m. The film with a latent image is separated fromthe selenium layer and external surface of the film is washed with aliquid electrophotographic developer for 5 to 10 seconds. As a result, apositive image of the original is produced having uniformly developedcontinuous sections.

EXAMPLE 5

A lined original is reproduced as described in Example 4, but thedeveloper is applied to both sides of the film. As a result, direct andreverse images of the original are obtained on the two surfaces of thefilm.

EXAMPLE 6

A tone original with a range of optical densities from 0.05 to 1.95 isreproduced as described in Example 4 but with an exposure of 20-25seconds. As a result, an image is produced with adequate tonetransmission within a density interval from 0.05 to 1.3 and without afringe effect on the image. The film is separated from the seleniumlayer during the exposure. If fogging appears, the housing of the staticeliminator is insulated from the selenium layer substrate.

Compared to the known methods, the use of the proposedelectrophotographic method of producing an image described in Examples 4to 6 makes it possible to obtain diapositives featured by high sharpnessof the image with uniform reproduction of continuous fields and hightechnological parameters of the process due to essential simplificationof this process.

EXAMPLE 7

A lined positive original is reproduced as described in Example 4 butthe film with a latent image is separated from the selenium layer atnon-actinic illumination thus preserving the latent image on theselenium layer.

EXAMPLE 8

A positive lined original is reproduced as described in Example 7 but astatic eliminator is used providing a sliding discharge. This eliminatoris made by winding a wire coil around a piece of an insulated wire, ana-c voltage of 2 to 8 kV being applied to the wire and the coilconnected to the selenium layer. The operating time of the staticeliminator at a distance of 100 mm is equal to 1-2 sec. If foggingappears, the static eliminator body is insulated from the seleniumlayer.

EXAMPLE 9

The lined original is reproduced as described in Examples 7 and 8 butthe developer is fed to both sides of the film by immersing the latterinto a vertical metal cuvette. As a result, on both sides of the filmthere is produced a positive original image without a fringe effect onthe continuous fields.

EXAMPLE 10

A tone original with a set of optical densities from 0.15 to 1.50 isreproduced as described in Examples 7 and 8 but with an exposure of10-15 seconds. As a result, an image is produced within a densityinterval of 0.15 to 1.2 with adequate tone reproduction and with nofringe effect.

Compared to the existing methods of producing image, the proposedelectrophotographic method described in Examples 7 to 10 provides apossibility of multiple reproduction of lined and tone images by meansof one-time photography of the original with uniform reproduction of thecontinuous fields of the image.

EXAMPLE 11

A lined positive original with optical density of 1.45 and a backgrounddensity of 0.15 is reproduced using a copying apparatus. The seleniumplate with a layer about 50 μm thick is charged positively to apotential of 360 V and then exposed during 60 seconds with an apertureof 1:22. The exposed plate is transferred to a room with non-actinicillumination, where a sheet of triacetate film 25 μm thick is applied onthe selenium layer in a vacuum frame. After the complete contact withthe entire surface of the layer has been achieved, a radioisotope staticeliminator is placed above the selenium layer at a distance of 30 mm,the body of the static eliminator being connected with the substrate ofthe selenium layer. The film on the selenium layer is irradiated by thestatic eliminator during 5-10 seconds. Then the selenium layer with thefilm is placed into a medium of gaseous trichlorofluoromethane. The filmwith a latent image is separated from the layer at non-actinicillumination and the external surface of the film is drenched with aliquid electrophotographic developer during 5-10 seconds. As a result, apositive image of the original is obtained with uniformly developedsections with optical density of the line, D, equal to 2.6-2.8 and acoefficient γ of contrast equal to 10.

EXAMPLE 12

The reproduction and development are effected as described in Example 11but the charge of the selenium plates is taken equal to 500 V. In thiscase the film is separated from the selenium layer in liquidtrifluorotrichlorethylene.

As a result, a positive image of the original is obtained havinguniformly developed continuous sections with optical density (D) of theline equal to 2.8-3.0 and a contrast coefficient γ equal to 12.

EXAMPLE 13

The reproduction and development are conducted as described in Examples11 and 12 but the selenium plates are charged to 1000 V. In this casethe film is separated from the selenium layer in a gaseous medium usingcarbon tetrachloride. As a result, a positive image of the original isobtained with uniformly developed continuous sections with opticaldensity D of the line equal to 3 to 3.5 and a contrast coefficient γequal to 15.

Compared to the known methods, the use of the proposedelectrophotographic method for producing an image described in Examples11 to 13 makes it possible to copy originals having poor contrast of theimage.

INDUSTRIAL APPLICABILITY

The disclosed electrophotographic method for producing an image on adielectric film may be used mainly in polygraphy for obtaining lineimages used as templates when copying a printing plate on a lightsensitive material. Furthermore, the method makes it possible to obtaintone and raster images also used in polygraphy and in other areas ofcopying engineering. The method can be used for obtaining single lineand tone images of transparent materials used in cartography, aerialphotography, microphotography, etc.

I claim:
 1. An electrophotographic method for producing an image on adielectric film, in which the dielectric film is contacted with thesurface of a charged and exposed electrophotographic layer, the latentimage on the film is developed and fixed, characterized in that afterthe dielectic film (3) is contacted with the electrophotographic layer,the dielectric film (3) is acted on by positive and negative ions of thesame concentration from a source (4) of ions which settle on the film(3) and produce a latent image thereon; before the development of thislatent image the electrophotographic layer is illuminated by an actiniclight source (5).
 2. An electrophotographic method according to claim 1,characterized in that during and after the illumination of theelectrophotographic layer by the actinic light source (5) the dielectricfilm (3) is separated from the electrophotographic layer for eliminatingthe fringe effect during the subsequent development of the once-exposedlatent image being reproduced.
 3. An electrophotographic method forobtaining an image on a dielectric film, in which the dielectric film iscontacted with the surface of the charged and exposedelectrophotographic layer, the image obtained on the film is developedand fixed, characterized in that after the dielectric film (3) has beencontacted with the electrophotographic layer, the dielectric film (3) isacted on by positive and negative ions of the same concentration fromthe source (4) of ions, which settle on the film (3) and produce alatent image thereon; after that the dielectric layer film (3) isseparated from the electrophotographic layer illuminated by anon-actinic light source (8) for eliminating the fringe effect duringthe development of the multiple-reproduced image.
 4. Anelectrophotographic method according to any of claims 2 or 3,characterized in that the charge of the latent image on the dielectricfilm (3) is increased by raising the potential of the charge of theelectrophotographic layer, the dielectric film (3) being separated fromthe electrophotographic layer in an electrically inert medium preventingorigination of discharge between this film (3) and theelectrophotographic layer.
 5. An electrophotographic method according toclaim 4, characterized in that the electrically inert medium consist ofchlorine derivatives of hydrocarbons of the aliphatic series offluorinechloroderivatives of hydrocarbons of the same series.